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The Early Human Testing Initiative (EHTI) Phase I Human Test, performed by the Crew and Thermal Systems Division at Johnson Space Center, demonstrated the ability of a crop of wheat to provide air revitalization for a human test subject for a 15-day period. The test demonstrated three different methods for control of oxygen and carbon dioxide concentrations for the human/plant system and obtained data on trace contaminants generated by both the human and plants during the test and their effects on each other. The crop was planted in the Variable Pressure Growth Chamber (VPGC) on July 24, 1995 and the test subject entered the adjoining airlock on day 17 of the wheat's growth cycle. The test subject stayed in the chamber for a total of 15 days, 1 hour and 20 minutes. Air was mixed between the plant chamber and airlock to provide oxygen to the test subject and carbon dioxide to the plants by an interchamber ventilation system.

The Crew and Thermal Systems Division (CTSD) at NASA's Johnson Space Center under the support of the Office of Life and Microgravity Sciences and Applications is conducting the Early Human Testing Initiave (EHTI) project with the goal of validating regenerative life support technologies through a series of integrated tests with human subjects. The EHTI project is organized into three distinct phases, each with progressively more complex integration of biological and physicochemical (P/C) life support technologies. The goal of Phase I is to conduct a 15-day one-person test to verify the performance of an air revitalization system based on higher plants with physicochemical systems as complements and backups. The test will be performed in CTSD's Variable Pressure Growth Chamber (VPGC), a tightly closed controlled-environment test chamber configured with approximately 11 m2 of area for plant growth.

The Lunar-Mars Life Support Systems Test Project's Phase iii Test utilized the Variable Pressure Growth Chamber to contribute to the air revitalization and food requirements of a crew of four for a period of 91 days. USU-Apogee wheat was planted and harvested using a staged approach to provide more uniform levels of air revitalization and a staggered production of grain. The wheat crop provided an average of 1 .1 person-equivalents per day of carbon dioxide removal for air revitalization over the 91 -day human test. Over 34 kg of grain was harvested. it was found that staged cropping required more intensive management of the nutrient solution than single batch cropping. it was also found that salts which were biologically recovered from the plant biomass were as effective as conventional reagent-grade salts for use in the hydroponic nutrient solution.

Two crops of lettuce (Lactuca sativa cv. Waldmann's Green) were grown in the Regenerative Life Support Systems (RLSS) Test Bed at NASA's Johnson Space Center. The RLSS Test Bed is an atmospherically closed, controlled environment facility for the evaluation of regenerative life support systems using higher plants. The chamber encloses 10.6 m2 of growth area under cool-white fluorescent lamps. Lettuce was double seeded in 480 pots, each containing about 250 cm3 of calcined-clay substrate. Each pot was irrigated with half-strength Hoagland's nutrient solution at an average total applied amount of 2.5 and 1.8 liters pot-1, respectively, over each of the two 30-day crop tests. Average environmental and cultural conditions during both tests were 23°C air temperature, 72% relative humidity, 1000 ppm carbon dioxide (CO2), 16h light/8h dark photoperiod, and 356 μmol m-2s-1 photosynthetic photon flux.